The IKs delayed rectifier potassium current is critical for cardiac action potential repolarization. The channel that carries the IKs current has pore-forming a subunits encoded by the KCNQ1 gene, and regulatory [unreadable] subunits encoded by the KCNE1 gene. Interactions between these subunits regulate the current, allowing adaptation to changes in heart rate. Hundreds of mutations identified in the two genes have been associated with Long QT Syndrome (LQTS) and Familial Atrial Fibrillation (FAF), both of which increase the risk of potentially fatal arrhythmias in patients. The goal of this project is to determine the structure-function relationships between KCNQ1 and KCNE1, with particular attention to how the interactions between the C- termini of the subunits influence IKs kinetics and adaptation to heart rate changes (Aim #1),and how mutations alter these interactions resulting in disease phenotypes (Aim #2).Site-directed mutagenesis will target predicted areas of interaction, with functional studies carried out via whole-cell patch clamping to determine current densities, gating kinetics, and voltage dependence of gating. Specific sites of contact between the two C-termini will be determined by hydrogen/deuterium exchange mass spectrometry and thermodynamic double-mutant cycle analysis. The sites of contact will be biochemically characterized, with subtle changes in binding affinity quantified by surface plasmon resonance analysis. Mutagenesis will be used to introduce known LQTS mutations in the KCNQ1 and KCNE1 C-termni, to explore the structural basis of LQTS phenotypes. Arrhythmias, or disorders of the regular rhythmic beating of the heart, are responsible for 300,000 to 400,000 cases of sudden death per year in the USA. PUBLIC HEALTH RELEVANCE: Our research examines the interaction of two cardiac proteins that stabilize the heart rhythm during exercise and how mutations in these proteins lead to an increased risk of arrhythmias in patients. A better understanding of these proteins will likely contribute to advances in diagnosis and treatment of arrhythmias.